United States Patent 6,126,968 Landscape: Scope, Claim-by-Claim Coverage and Expiry/Design-Around Routes for R(+)-N-propargyl-1-aminoindan Tablet Formulations
Executive summary
U.S. Patent 6,126,968 is a formulation patent focused on tablet compositions containing R(+)-N-propargyl-1-aminoindan (or a pharmaceutically acceptable salt) combined with high proportions of specific polyhydric alcohol excipients (pentahydric/hexahydric, with core exemplars mannitol, xylitol, sorbitol) and optionally citric acid and magnesium stearate. The claims are drafted around (i) excipient identity, (ii) excipient content thresholds (notably ≥60% or ≥75% by weight), and (iii) optional additives with narrow ranges (citric acid 0.5–2%; magnesium stearate 0.1–0.5%). For generic or follow-on formulation developers, the primary “hard” design-around levers are changing alcohol type, dropping below the stated weight fractions, changing the acid/magnesium excipient system, and/or moving away from a tablet form if other claim types exist in the full patent.
What does US 6,126,968 claim cover for R(+)-N-propargyl-1-aminoindan tablets?
Core claimed subject matter (plain-English)
A tablet formulation that includes:
- A therapeutically effective amount of R(+)-N-propargyl-1-aminoindan or a pharmaceutically acceptable salt
- At least one alcohol selected from pentahydric and hexahydric alcohols
- Optional but claimed components:
- Citric acid (with a defined 0.5–2% by weight range in dependent claims)
- Magnesium stearate (with a defined 0.1–0.5% by weight range in dependent claims)
Claim scope is excipient-driven
The independent coverage hinges on the combination of (a) the active ingredient and (b) a specific alcohol excipient class with high weight percent content. Dependent claims tighten these by:
- Minimum alcohol mass fraction (≥60% or ≥75%)
- Alcohol species restrictions (mannitol, xylitol, sorbitol)
- Quantitative ranges for citric acid and magnesium stearate
- A cap on active content in some embodiments (active ≤3.0% by weight)
Claim-by-claim scope map (US 6,126,968 as provided)
| Claim |
Form factor |
Active ingredient requirement |
Alcohol requirement |
Optional components |
Key quantitative limits |
| 1 |
Tablet |
R(+)-N-propargyl-1-aminoindan or salt; “therapeutically effective amount” |
At least one pentahydric/hexahydric alcohol |
None required |
Alcohol wt% not specified in claim 1 |
| 2 |
Tablet |
Same as claim 1 |
Alcohol wt% at least 60% |
None required |
Alcohol ≥60% (of total composition) |
| 3 |
Tablet |
Same as claim 1 |
Alcohol must be mannitol or xylitol or sorbitol |
None required |
None beyond identity |
| 4 |
Tablet |
Same as claim 1 |
Same alcohol requirement as claim 1 |
Citric acid added |
Citric acid range in claim 5 |
| 5 |
Tablet |
Same as claim 4 |
Same alcohol requirement as claim 1/2? (as dependent structure implies) |
Citric acid |
Citric acid 0.5–2% by weight |
| 6 |
Tablet |
Same as claim 1 |
Same as claim 1 |
Magnesium stearate added |
None in claim 6 |
| 7 |
Tablet |
Same as claim 6 |
Same as claim 1 |
Magnesium stearate |
Magnesium stearate 0.1–0.5% by weight |
| 8 |
Tablet |
Same as claim 1 |
Alcohol between 60–70% and citric acid present |
Citric acid |
Alcohol 60–70%, citric acid present |
| 9 |
Tablet |
Active explicitly named |
Same as claim 1 |
None required |
No added numerical limits |
| 10 |
Tablet |
Active + salt present |
At least 75% by weight of at least one alcohol from mannitol/xylitol/sorbitol |
None required |
Alcohol ≥75% |
| 11 |
Tablet |
Active ≤3.0% by weight |
Alcohol ≥75% by weight |
None required |
Active ≤3.0%; alcohol ≥75% |
| 12 |
Tablet |
Same as claim 10 (dependent) |
Alcohol is mannitol |
None required |
None beyond identity |
| 13 |
Tablet |
Active or salt |
At least one pentahydric/hexahydric alcohol |
None required |
Alcohol wt% not specified in claim 13 |
| 14 |
Tablet |
Same as claim 13 |
Alcohol ≥60% |
None required |
Alcohol ≥60% |
| 15 |
Tablet |
Same as claim 13 |
Alcohol is mannitol/xylitol/sorbitol |
None required |
None beyond identity |
| 16 |
Tablet |
Same as claim 13 |
Same alcohol requirement |
Citric acid added |
Citric acid range in claim 17 |
| 17 |
Tablet |
Same as claim 16 |
Same |
Citric acid |
Citric acid 0.5–2% by weight |
| 18 |
Tablet |
Same as claim 13 |
Same |
Magnesium stearate added |
Magnesium range in claim 19 |
| 19 |
Tablet |
Same as claim 18 |
Same |
Magnesium stearate |
Magnesium stearate 0.1–0.5% by weight |
| 20 |
Tablet |
Same as claim 13 |
Alcohol 60–70% and citric acid present |
Citric acid |
Alcohol 60–70% |
| 21 |
Tablet |
Active explicitly named |
Same as claim 13 |
None required |
No added numerical limits |
| 22 |
Tablet |
Active + salt |
Alcohol ≥75% (mannitol/xylitol/sorbitol) |
None required |
Alcohol ≥75% |
| 23 |
Tablet |
Active ≤3.0% by weight |
Alcohol ≥75% |
None required |
Active ≤3.0%; alcohol ≥75% |
| 24 |
Tablet |
Same as claim 22 |
Alcohol is mannitol |
None required |
None beyond identity |
| 25 |
Tablet |
Active ≤3.0% by weight |
Depends on claim 2 |
None required |
Active ≤3.0%; alcohol ≥60% (from claim 2) |
| 26 |
Tablet |
Active ≤3.0% by weight |
Depends on claim 14 |
None required |
Active ≤3.0%; alcohol ≥60% (from claim 14) |
What this means for practical coverage
- If a competitor’s tablet uses mannitol/xylitol/sorbitol at ≥60% or ≥75% and includes R(+)-N-propargyl-1-aminoindan (or salt) at any amount consistent with “therapeutically effective,” they are exposed to the alcohol-threshold dependent claims.
- If the formulation includes citric acid at 0.5–2% while using the high alcohol fraction system, the exposure deepens.
- If the formulation includes magnesium stearate at 0.1–0.5%, exposure extends to those dependent embodiments.
- The explicit active ≤3.0% limitations appear only in specific dependent claims, which can reduce risk for very high-dose tablets (though those would still need to be evaluated under the independent claims that do not cap active content).
What alcohol excipients are protected under US 6,126,968?
Excipients explicitly within the claim language
- Alcohol class: pentahydric and hexahydric alcohols
- Explicit exemplars: mannitol, xylitol, sorbitol
Weight fraction thresholds that drive infringement risk
- Claim 2/14/25/26: alcohol ≥60% by weight
- Claim 10/11/12/22/23/24: alcohol ≥75% by weight
- Claim 8/20: alcohol 60–70% by weight (with citric acid present in those embodiments)
How “at least one alcohol” affects design-around
Claims use “at least one alcohol selected from the group consisting of ….” In practice, a formulation with only one listed alcohol and meeting the thresholds is squarely within the claim. A formulation with a listed alcohol plus other alcohols can still infringe if the listed alcohol content meets the threshold language depending on how the competitor calculates “at least one alcohol” contribution. The cleanest risk reduction is to avoid meeting the thresholds with the specifically listed alcohols.
Do the claims require citric acid and magnesium stearate?
Citric acid
- Not required in claim 1.
- Becomes required in dependent claims 4, 5, 8, 16, 17, 20.
- When required, citric acid has a tight quantitative definition in claims 5 and 17: 0.5 to 2% by weight.
Magnesium stearate
- Not required in claim 1.
- Appears in dependent claims 6, 7, 18, 19.
- Tight range in claims 7 and 19: 0.1 to 0.5% by weight.
Infringement exposure logic
- A competitor can materially change risk by omitting citric acid entirely, or by using a different acid at a different concentration, or by using citric acid outside 0.5–2%.
- For magnesium stearate, similar risk reduction exists by omitting it or moving outside 0.1–0.5%. If magnesium stearate is needed for manufacturing, switching magnesium stearate to another lubricant, or changing dose, is the main lever.
How much active ingredient is covered, and does US 6,126,968 cap dose?
No active cap in independent claim 1 as provided
- Claim 1 requires a “therapeutically effective amount” without a numeric upper bound.
- Claims 9 and 21 merely specify the active as R(+)-N-propargyl-1-aminoindan (not an salt).
Active cap appears only in specific dependent claims
- Claims 11, 23, 25, 26 state:
- Active (or salt) amount is 3.0% or less by weight.
- Combined with alcohol thresholds (≥75% for 11/23; ≥60% for 25/26).
Commercial implication
- If a tablet contains R(+)-N-propargyl-1-aminoindan above 3% by weight, it may fall outside those dependent claims but could still infringe independent claims 1/13 or other dependent claims not containing the cap (2/3/4/8/14/15/16/18/20 etc.). The active cap is not the core determinant of infringement because the highest-level claims are excipient-class and tablet-form focused.
What is the likely claim “center of gravity” for infringement risk?
Highest-probability infringement fact patterns
- Tablet using mannitol/xylitol/sorbitol as the primary excipient at ≥60% and optionally including:
- citric acid at 0.5–2%, and/or
- magnesium stearate at 0.1–0.5%
- Tablet using mannitol/xylitol/sorbitol at ≥75%, with active potentially low (≤3%) but not required by all claims.
Why the 60% and 75% thresholds matter
These thresholds convert formulation into a narrow compositional envelope. Generic developers who maintain high-lactose systems or lower-alcohol systems are outside the claim space. Tablet excipient systems that are heavily polyol-based (common for direct compression) are most exposed.
What design-around strategies are available against US 6,126,968’s claim structure?
1) Avoid the protected alcohol species
- Replace the polyhydric alcohol system so it does not use mannitol/xylitol/sorbitol as the primary alcohol meeting the claimed thresholds.
- Use a different alcohol outside the “pentahydric and hexahydric” definitions, or a mixture where the listed alcohol content does not reach the claimed mass fraction.
2) Drop below the protected alcohol weight fractions
- If the formulation uses mannitol/xylitol/sorbitol, keep the relevant alcohol (as “at least one alcohol selected from the group…”) below 60% or below 75%, depending on whether the intended product could be evaluated under those dependent claim versions.
- For embodiments with a 60–70% bracket (claims 8 and 20), avoid that range in combination with citric acid presence.
3) Move citric acid concentration out of 0.5–2% or omit citric acid
- Avoid the specific citric acid 0.5–2% ranges that are explicitly claimed.
4) Move magnesium stearate out of 0.1–0.5% or omit
- Use a different lubricant system, or change magnesium stearate dose outside the claimed range.
5) Change dosage form
- These claims explicitly require “tablet form.” If a development targets capsules, oral dispersible formulations, or other dosage forms, it is outside the claim language as provided.
What is the patent estate strength implied by the claims, and where are the vulnerabilities?
Strength characteristics
- The patent covers specific excipient compositions with high quantitative thresholds. These tend to be harder for generic programs to avoid if they copy the same formulation strategy.
- The claims are layered: independent claims capture the core system; dependent claims add tight constraints around citric acid and magnesium stearate.
Vulnerabilities
- The claims are composition-in-a-box. If a competitor can:
- shift excipient selection,
- lower polyol fraction below the stated thresholds,
- or alter citric acid/magnesium stearate dosing,
then the literal claim path narrows quickly.
- The patent as provided does not show:
- polymorph or solid-state form claims,
- process/manufacturing claims,
- or method-of-use claims.
If those exist elsewhere in the same patent, they are not visible in the claim list provided.
What Orange Book status and FDA exclusivity are relevant for this formulation patent?
No Orange Book status, application reference (NDA/ANDA/BLA), listed patents, or FDA exclusivity links are provided in the prompt; therefore no accurate determination can be made from the claim text alone.
What generic entry risks exist for R(+)-N-propargyl-1-aminoindan tablet products?
High-risk scenario
A follow-on manufacturer files an ANDA (or otherwise markets a tablet) that uses:
- R(+)-N-propargyl-1-aminoindan (or salt)
- a high polyol system of mannitol/xylitol/sorbitol
- meeting ≥60% or ≥75%
- and optionally includes citric acid and/or magnesium stearate within the claimed ranges
Lower-risk scenario
A formulation uses:
- different excipients,
- or polyol content below thresholds,
- and/or citric acid and magnesium stearate outside the specified ranges.
How many distinct formulation “sub-bundles” does US 6,126,968 effectively define?
Based on the provided claims, the patent defines at least four practical sub-bundles:
-
Tablet with pentahydric/hexahydric alcohols (core)
-
High alcohol fraction (≥60%) using allowed alcohol species
- Claims 2/3/14/15 and related active cap versions (25/26)
-
Very high alcohol fraction (≥75%) using allowed alcohol species
- Claims 10/11/12 and 22/23/24
-
High alcohol fraction plus citric acid and/or magnesium stearate at claimed concentrations
- Citric acid: claims 4/5/8/16/17/20
- Magnesium stearate: claims 6/7/18/19
What jurisdictions and enforcement relevance follow from this being a US patent?
The claims provided are for a United States patent. Enforceability and litigation strategy are US-specific (e.g., Orange Book listing, infringement in US, venue). No foreign counterpart patents are identified in the prompt, and no family information is supplied; therefore no cross-jurisdictional enforcement map can be produced from the claim text alone.
Key Takeaways
- U.S. 6,126,968 is a tablet formulation patent built around R(+)-N-propargyl-1-aminoindan (or salt) plus high-percentage pentahydric/hexahydric alcohol excipients, with explicit emphasis on mannitol, xylitol, sorbitol.
- The claim-dominant risk thresholds are alcohol ≥60% and alcohol ≥75% by weight; additional dependent limits include:
- citric acid 0.5–2% by weight
- magnesium stearate 0.1–0.5% by weight
- active ≤3.0% by weight in select dependent claims
- Design-around is primarily compositional:
- change alcohol identity,
- reduce the listed alcohol fraction below 60%/75%,
- omit or move citric acid outside 0.5–2%,
- omit or move magnesium stearate outside 0.1–0.5%,
- or change dosage form away from “tablet.”
FAQs
1) Does US 6,126,968 cover tablets with polyhydric alcohols other than mannitol, xylitol, and sorbitol?
Yes at the class level: claims cover pentahydric and hexahydric alcohols broadly (claims 1, 13). Species-specific restriction to mannitol/xylitol/sorbitol appears in dependent claims (e.g., 3, 15, 12, 24, 10/22).
2) If a tablet contains ≥60% mannitol but no citric acid, is it still potentially infringing?
Yes. Citric acid is only in dependent claims. Claims 1/2/3 (and 13/14/15) can still be implicated without citric acid.
3) If a tablet uses mannitol at 58% and includes citric acid 1%, does it avoid the ≥60% alcohol claims?
It avoids claims that require alcohol ≥60%. It would still need evaluation against any claims with different thresholds (notably ≥75%) and against the core independent claim language.
4) How do the 60–70% alcohol and citric acid combination claims change formulation strategy?
They create a tighter compositional window: avoid 60–70% alcohol while also having citric acid if the formulation would otherwise align with those dependent claims (claims 8 and 20).
5) Does the active ingredient dose cap (3.0% or less) apply to all claims?
No. The ≤3.0% limit appears only in select dependent claims (11, 23, 25, 26). Other dependent and independent claims do not state an active % cap.
References
- United States Patent 6,126,968.
